In dry climates, evaporative coolers can be a more efficient alternative to a compressor-based air conditioner for creating comfortable indoor conditions. The simplest evaporative coolers, often called either direct evaporative coolers or swamp coolers, flow dry, hot outdoor air through a wetted, porous pad. The evaporation that occurs in the pad both drops the temperature and increases the humidity of the air. The lowest temperature that can be achieved in a direct evaporative cooler is the wet-bulb temperature of the entering air.
Indirect evaporative coolers improve upon simple swamp coolers by using a heat exchanger to separate the process air that is to be delivered to the building from a second air stream that evaporates water to produce a cooling effect. The two air streams flow on opposite sides of the heat exchanger so the process air is cooled without gaining humidity. However, as with the direct evaporative cooler, the wet-bulb temperature of the cooling air sets the lower limit for the temperature of the delivered process air.
In 1939, W. M. Niehart received U.S. Pat. No. 2,174,060 for an improved indirect evaporative cooler in which the cooling air itself is first evaporatively cooled before it comes in contact with the wetted surface of the indirect evaporative cooler. Because the wet-bulb temperature of the cooling air has been lowered before it contacts the wetted surface, Niehart's invention can cool the process air to a temperature that is below the initial wet-bulb temperature of the cooling air. In most applications, the initial dewpoint temperature of the cooling air is the lower limit for the temperature of the delivered process air. Since the air's dewpoint temperature is always lower than its wet-bulb temperature when the air is unsaturated, Niehart's invention, which will be referred to as a dewpoint indirect evaporative cooler (DIEC), can supply air at a lower temperature than a conventional indirect evaporative cooler.
In 1955, V. Maisotsenko received U.S. Pat. No. 5,453,223 for an alternative configuration of a DIEC. Coolerado Corporation of Denver, Colo., USA now manufactures and sells a DIEC based on the technology invented by Maisotsenko. Seeley International of Adelaide, South Australia and StatiqCooling BV of Amsterdam, Netherlands now manufacture and sell DIECs that more closely embody the principals illustrated in the Niehart patent.